Davis, Randy

Zhang, Hailin

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OKLAHOMA COOPERATIVE       EXTENSION SERVICE PRODUCTION TECHNOLOGY PT 2001-21   August 2001 Plant Nutrients in Rainfall  Randy Davis and Hailin Zhang Department of Plant and Soil Sciences   It’s commonly known that rainfall contains some essential plant nutrients.  However, many people don’t know which nutrients and just how much are supplied by rainfall.  These facts beg many questions, such as; how can plant nutrients in rainfall affect producers, how can producers take advantage of plant nutrients in rainfall, and, is acid rain a problem in Oklahoma?   A study conducted in the mid 1980’s at various locations across the Southern Plains concluded that inputs of Nitrogen (N) and sulfur (as SO4) from rainfall could contribute considerable amounts of these nutrients for plant use.  However, rainfall doesn’t contain significant amounts of phosphorus (P), potassium (K), chloride (Cl), and the other essential plant nutrients.  Nitrogen is often the most limiting nutrient for crop production in Oklahoma.  Each year producers spend millions of dollars on nitrogen fertilizers.  Although rainfall adds a small amount of nitrogen to the Oklahoma landscape, it cannot be relied upon as the only source of nitrogen needed for high production farming. Nitrogen in rainfall occurs in mostly equal parts nitrate and ammonium (as in NO3-N and NH4-N).  Together, they add about 7 pounds plant available nitrogen (PAN) per acre each year (see table below).  As most producers know, this is a very small amount of nitrogen compared to the amount needed to produce an average non-legume crop.  However, the small amount of N supplied by rain may be very useful in those years when environmental conditions are better than average and the crop could use just a little extra N to push it above an average yield.  Average Amount of Nutrients from Rainfall in Central Oklahoma Location pH Nitrate - N Ammonium - N Total PAN Sulfate - S Chloride - Cl   ______________________________________________lbs/acre/year_________________________________ El Reno 6.5 3.0 2.9 5.9 51 7.6 Woodward 6.5 2.3 3.0 5.3 78 14 Chichasha 6.7 6.0 3.4 9.4 75 -- Average 6.6 3.8 3.1 6.9 68 11 Adopted from Sharpley et al., 1985. The chemical composition of rainfall in the Southern Plains and it’s impact on soil and water quality. Technical Bulletin T-162, Oklahoma Agricultural Experiment Station, Oklahoma State University.  In addition to N, rainfall provides about 70 pounds sulfur per acre each year.  This is more than enough sulfur needed by most plant species, since plants only need one part sulfur for every 20 parts of N.  These values listed in the table above were collected from the central portion of Oklahoma.  As rainfall amount decreases from eastern to western Oklahoma, nutrient amounts will also vary.  Eastern Oklahoma should expect higher amount of nutrients from precipitation than those in western Oklahoma. Recently, scientists have reported the occurrence of acid rain in some parts of the United States.  On most of the research sites in Oklahoma, rainfall was near neutral.  This suggests rainfall in Oklahoma will have little or no impact on soil pH.   Oklahoma State University, in compliance with Title VI and Vii of the Civil Rights Act of 1964, Executive Order 11246 as amended, Title IX of the Education Amendments of 1972, Americans with Disabilities Act of 1990, and other federal laws and regulations, does not discriminate on the basis of race, color, national origin, sex, age, religion, disability or status as a veteran in any of its policies, practices or procedures.  This includes but is not limited to admissions, employment, financial aid, and educational services.  Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1913, in cooperation with the US Department of Agriculture, Sam E. Curl, Director of Oklahoma Cooperative Extension Service, Oklahoma State University, Stillwater, Oklahoma.  This publication is printed and issued by Oklahoma State University as authorized by the Dean of the Division of Agricultural Sciences and Natural Resources.  Oklahoma State University       PT 2001-21                                       Vol. 13 No. 21  

Plant nutrients in rainfall

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Plant nutrients in rainfall

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